The present invention relates to mixing apparatus and more particularly to impellers for use in such mixing apparatus.
Such mixing apparatus employs an impeller to impart flow and turbulence to a fluid medium in order to produce in such medium the stirring of a mixture, an aeration, a mixing or dispersive action. It is known that high efficiency liquid pumping action may be facilitated by the use of an impeller having blades with a hydrofoil shape. Such impellers have been fabricated from plates, such as disclosed in U.S. Pat. No. 4,147,437, issued Apr. 3, 1979. Such impellers may additionally have pitched blades in which the blade angle with respect to a plane perpendicular to the shaft increases from the tip to the base; and at least the outer portion of the blades have a camber as depicted in FIG. 5.
The methods used to construct pitched blade hydrofoil impellers have been complex and expensive. Even those impellers utilizing blades fabricated from plates are relatively difficult to manufacture. Much of this difficulty is attributable to the fact that the blades must not only be formed to a predetermined hydrofoil shape, the hub angle and tip angles must be precisely established since such have a significant impact on the performance of the impeller. One method of constructing such an impeller utilizes ears attached to the impeller hub at a predetermined hub angle. The desired root angle is established when the root of the impeller blade is attached to the ear. However, even though root angle may be precisely established in this manner, a final twist operation is frequently required to achieve an accurate tip angle. Such a fabrication process frequently requires multiple twist operations in order to finally establish the correct tip angle with respect to the root angle established by the hub ear. Another, but considerably more expensive process, entails casting the impeller utilizing a mold having accurately established root and tip angles.
It is known that input power spikes can occur when the level of the liquid in which the impeller is immersed approaches the level of the impeller blades, while raising or lowering the liquid level. An impeller having drooping blades was found to reduce or eliminate this power spike. The blade droop has been obtained by using downward angled hub ears to which the blades are attached, which is an expensive option. In another configuration, the blades are set at a severe angle to the hub ear such as, for example, shown in U.S. Pat. No. 4,147,437, FIG. 6. The disadvantages of these types of constructions include increased expense and difficulty of attaining accurate tip angles.
Accordingly, it is an object of the present invention to provide an impeller having a high efficiency liquid pumping action and enhanced power stability.
It is another object of the present invention to provide an impeller having low power requirements for a given speed and diameter.
It is yet another object of the present invention to provide an impeller having blades which are relatively easily manufactured.
It is a further object of the present invention to provide an impeller having blades which may be formed from cut plate with an accurate tip angle produced.